The present invention relates generally to electronic counter measures and specifically to electronic countermeasures for protecting mobile platforms against radio frequency threats. Radar systems, typically use electromagnetic waves to identify characteristics, such as range, altitude, direction, and/or speed, of moving objects, such as aircrafts and ships. Such radar systems may support surface-to-air missiles (“SAM”) and anti-aircraft armament (“AAA”). Radar system antennae typically transmit pulses of radio waves or microwaves. A portion of these pulsed waves can be reflected from objects that are in the wave's path (or sidelobes of the radar's antenna), and returned to the antenna, wherein the associated radar system detects and measures the reflected waves. Using the time it takes for the reflected waves to return to the antenna and additional signal processing techniques, a radar system computer can calculate how far away the object is, its radial velocity and other characteristics. Transmitters and receivers for such systems can be separate entities (“bistatic”) or may exist as co-located unified systems.
Electronic counter measures (“ECM”) may include electrical devices that can be designed to nullify or reduce the effectiveness of radar systems. ECMs may be deployed defensively and/or offensively to deny and/or reduce the ability to generate targeting, tracking, identification, and/or positioning information. One form of radar countermeasures is the use of chaff. Chaff may be dispersed as clouds of resonant dipoles into the atmosphere to create a high radar return zone to mask the presence and/or location of an object. Chaff is typically a passive ECM that can be comprised of shredded aluminum foil and/or a glass substrate coated with aluminum. Chaff can have an average overall diameter of around 25 microns. Chaff can be deployed offensively and/or defensively.
Chaff can be employed as a “decoy” or to disrupt the tracking radar lock-on function of, for example, a fire control anti-aircraft armament or missile system. The individual aluminized glass fibers can form electromagnetic dipoles. Effectively, chaff are passive reradiating antennae. The principles on which radar impairment is based are similar whether the radar system is monostatic or bistatic. The main idea is to cause a relatively large amount of energy, dispersed in both angle and range, to be reflected to the receiver with energetic energy sufficient to dominate (i.e. mask) the return signal from the object (i.e. the signal related to object scattering).